1. Technical Field of the Invention
The present invention relates to novel cosmetic compositions for topical application, for the photoprotection of the skin and/or the hair against ultraviolet radiation (such compositions hereinafter simply designated "sunscreen," "sunscreen/cosmetic" or "photoprotective/sunscreen" compositions), and to the use of same for the cosmetic applications indicated above.
This invention more especially relates to the aforesaid sunscreen/cosmetic compositions comprising, in a cosmetically acceptable vehicle, carrier or diluent, typically an oil-in-water emulsion, combinatory immixture of (i) at least one of two particular solid lipophilic organic sunscreen compounds and (ii) at least one of two particular liquid lipophilic salicylate sunscreen compounds that solubilize said solid sunscreen compounds (i) therein.
2. Description of the Prior Art
It is well known to this art that light radiation of wavelengths of from 280 nm to 400 nm promotes tanning of the human epidermis, and that irradiation of wavelengths of from 280 to 320 nm, i.e., UV-B irradiation, causes erythema and burning of the skin which can impair the development of a natural tan; hence, such UV-B radiation must thus be screened from the skin.
It is also known to this art that UV-A radiation, of wavelengths from 320 to 400 nm, which tans the skin, also adversely affects it, in particular in the event of sensitive skin or a skin which is continually exposed to solar radiation.
UV-A rays cause, in particular, a loss in the elasticity of the skin and the appearance of wrinkles, promoting a premature aging thereof. Such irradiation promotes triggering of the erythematous reaction or enhances this reaction in certain individuals, and may even be the source of phototoxic or photoallergic reactions. Thus, it is desirable to also screen out UV-A radiation.
A wide variety of cosmetic compositions intended for the photoprotection (UV-A and/or UV-B) of human skin are known to this art.
These photoprotective/sunscreen compositions are typically oil-in-water emulsions (namely, a cosmetically acceptable vehicle, carrier or diluent comprising an aqueous continuous dispersing phase and an oily discontinuous dispersed phase) which contains, in various concentrations, one or more standard lipophilic and/or hydrophilic organic sunscreen compounds capable of selectively absorbing harmful or deleterious UV radiation. These sunscreen compounds (and the amounts thereof) are selected as a function of the desired sun protection factor (the sun protection factor (SPF) being expressed mathematically by the ratio of the irradiation time required to attain the erythema-forming threshold with the UV screening agent to the time required to attain the erythema-forming threshold in the absence of UV screening agent).
Two organic sunscreen compounds having desirable properties and which to date have been widely used are (1) 4-methylbenzylidenecamphor, which is commercially available and marketed under the trademark "EUSOLEX 6300" by Merck, and (2) 4-(tert-butyl)-4'-methoxydibenzoylmethane, also available commercially and marketed under the trademark "PARSOL 1789" by Givaudan.
These are two lipophilic sunscreen compounds, the first of which is highly active in the UV-B range and the second of which is highly active in the UV-A range, but which present the disadvantage of both being solid at room temperature. For this reason, incorporating same into sunscreen/cosmetic compositions, whether alone or in admixture, entails certain constraints as regards their formulation and application, in particular in the selection of the solvents permitting proper dissolution thereof. In this respect, solvent oils are typically employed, such as esters and in particular C.sub.12 -C.sub.15 alkyl benzoates ("Finsolv TN" marketed by Finetex), or triglycerides and in particular triglycerides of C.sub.8 -C.sub.12 fatty acids ("Miglyol 812" marketed by Huls), or, alternatively, of monoalcohols or polyols such as ethanol, or mixtures thereof. These oils nevertheless present certain disadvantages, in particular they exhibit no specific (or intrinsic) activity in respect of screening UV radiation (whether UV-A and/or UV-B), even though their solubilizing properties vis-a-vis the aforesaid two sunscreen compounds are adequate.